Index: llvm/lib/Analysis/CFG.cpp
===================================================================
--- llvm/lib/Analysis/CFG.cpp
+++ llvm/lib/Analysis/CFG.cpp
@@ -147,6 +147,8 @@
 
   const Loop *StopLoop = LI ? getOutermostLoop(LI, StopBB) : nullptr;
 
+  const DomTreeNode *StopNode = DT ? DT->getNode(StopBB) : nullptr;
+
   // Limit the number of blocks we visit. The goal is to avoid run-away compile
   // times on large CFGs without hampering sensible code. Arbitrarily chosen.
   unsigned Limit = 32;
@@ -159,7 +161,9 @@
       return true;
     if (ExclusionSet && ExclusionSet->count(BB))
       continue;
-    if (DT && DT->dominates(BB, StopBB))
+
+    DomTreeNode *DTN = StopNode ? DT->getNode(BB) : nullptr;
+    if (StopNode && DTN && DT->dominates(DTN, StopNode))
       return true;
 
     const Loop *Outer = nullptr;
@@ -186,6 +190,14 @@
       // any of these blocks, we can skip directly to the exits of the loop,
       // ignoring any other blocks inside the loop body.
       Outer->getExitBlocks(Worklist);
+    } else if (DTN) {
+      // The dominance check effectively visited all blocks dominated by BB.
+      // Skip over the descendants of the DomTreeNode to visit their successors.
+      for (auto I = df_begin(DTN), E = df_end(DTN); I != E; ++I) {
+        for (auto Succ : successors(I->getBlock()))
+          if (!DT->dominates(DTN, DT->getNode(Succ)))
+            Worklist.push_back(Succ);
+      }
     } else {
       Worklist.append(succ_begin(BB), succ_end(BB));
     }